1. Field of the Invention
The present invention relates to a pneumatic rotary drive.
2. Description of the Related Art
U.S. Pat. No. 4,838,148 discloses a pneumatic rotary drive in which a ring-shaped belt surrounds a stationary cylinder-shaped body, so that the belt assumes a kidney shape and forms pressure chambers. Depending on where pressure is applied, this kidney-shaped circular belt travels to one side or to the other side. At the respective end stop of the belt, the pressure chamber volume to which pressure medium is admitted is at a maximum and the pressure chamber volume to be vented is at a minimum, i.e. zero. In other words, the belt makes contact on one side with the cylinder-shaped body over half the circumference of the body and, thus, further yielding of the belt under the application of pressure can no longer occur. The movement of the belt under the application of pressure is transmitted to a shaft by means of toothings arranged on the outside of the belt. This known pneumatic rotary drive has the disadvantage that during operation at high angular velocities, a jerky and sudden deceleration of the rotary movement occurs at each stop. This has a disadvantageous effect on the support of the moveable elements and on the toothing itself. Moreover, because of the extremely high sudden tensile load acting on the belt, a shorter service life of the belt itself must be expected. This rotary drive utilizes a single stationary cylinder-shaped body or guide body.
U.S. application Ser. No. 07/861,228, U.S. Pat. No. 5,224,412 proposes a rotary drive with two guide bodies which are surrounded by a belt and are in operative connection with a shaft which extends to the outside. Depending on the respective end position assumed by the belt, the belt makes almost complete contact with the periphery of one of the guide bodies or with the periphery of the other of the guide bodies. In this rotary drive, a sudden deceleration also takes place when approaching the end stops.